Presently many types of electrical cables are designed with spirally wrapped wires as the electrically neutral return circuit or as metallic electrical shielding. In particular, these types of electrical cables are commonly used to transfer power underground. Typically, the spirally wrapped wires are uniformly spaced apart from each other when wrapped around an internal insulation shield for uniform charge distribution. However, during subsequent handling and use of the electrical cable, often the spirally wrapped wires are shifted. Moreover, even when the wires are being wrapped over the relatively slippery surface of the insulation shield, the wires sometimes slip and abut one another. Thus, when two wires abut one another a small void is formed between the sides of the two wires and the insulation shield they overlie. When an outer jacket is extruded over the wires, such voids may create channels for undesirable ingress of water and allow separation of the insulation shield from the outer jacket.
In addition, when the outer jacket is extruded over the insulation shield and the wires, the insulation shield can become soft, and thus, may be significantly indented by the wires. If the insulation shield becomes excessively indented by the wires, then the indendations make it more difficult to prepare the cable for splicing and create channels for ingress of water at a splice or terminal.
While many attempts have been made to provide electrical cable with spirally wrapped wires that do not shift or excessively indent the insulation shield, numerous disadvantages are present in these prior electrical cables. Thus, many of these prior electrical cables are either expensive to manufacture or do not adequately prevent indentation of the insulation shield or slippage of the wires. An example of an electrical cable having ribs integrally extruded with a semiconductive insulation layer and helically wrapped by wires is disclosed in U.S. Pat. No. 3,351,706to Gnerre et al, the disclosure of which is hereby incorporated herein by reference. When the insulation shield is extruded with integral ribs, as in Gnerre et al, it is not possible to select a material for the ribs having different properties from the material composing the insulation shield. Accordingly, when the hot outer jacket is extruded over the insulation shield and the helical wires, the insulation shield and ribs become soft and the wires tend to indent into the insulation shield, since the ribs and the insulation shield are composed of the same material and have the same softening or melting point.
In addition, the material composing the insulation shield in prior cables is usually a relatively slippery material. Thus if the ribs are composed of the same material they also tend to be slippery. Moreover, if ribs are applied to the insulation shield by an adhesive, then the ribs tend to separate from the insulation shield due to changes in temperature on the electrical cable during use.
Other examples of prior electrical cables including spirally wrapped wires are disclosed in the following U.S. Pat. Nos., the disclosures of which are hereby incorporated herein by reference: 1,880,060 to Wanamaker; 2,163,235 to Chatham; 3,760,812 to Timm et al; 3,794,750 to Garshick; 4,131,757 to Felkel; 4,157,452 to Pignataro et al; 4,719,320 to Strait, Jr.; and 4,803,309 to Marin et al.
Examples of other prior electrical cables are disclosed in the following foreign patents: British Patent No. 506,948 to Callender's Cable Construction Company, Ltd.; British Patent No. 3,622 to Smith; British Patent No. 851,549 to Higgitt; British Patent No. 864,842 to Standard Telephones and Cables Ltd.; German Patent No. 2,438,308 to Cable and Metal Gutehoffen; and German Patent Nos. 1,232,628 to Cie. Generale D'Electricite, and 3,120,146 to Siemens AG.